Rail pickups could be single coils or humbuckers. Rails have nothing to do with that. Most pickups including humbuckers and single coils have string magnets on which the coil is wounded. The advantage is their sensitivity. The disadvantage is that the vibrations of the string that happen right over the pole pieces are strong and when the vibrations when they are between the pole pieces are weak. This results in unveven picking up the vibrations by the pickup. This also leads to some dead spots. Another big problem is alingment. Not all the time, you will see all your strings placed exactly over the pole pieces. Since the magnet is strong, it makes the vibrations to stop early, so the natural sustain is cut down a bit.
Rails use weaker magnets, hence allowing the string to vibrate a lot and increasing sustain. They claim that it's more punchier than the pickups with pole pieces. I own both of them. I have Rail pickup as well as pickup with Pole pieces. Both of them are from big names in the industry but my humbucker with the pole pieces is definitely more punchier. By the way, in the rail, the magnet is also as a line, so there are no uneven picking up of vibrations and also there are no dead spots.
Finally it just boils down to what sound you like. I like my Pole piece humbucker much more than my other Dual Rail humbucker.
Yngwie uses something called Stacked Humbucker. It still is a humbucker but both the coils are kept one over the other, so that it can fit in that single coil slot. It still is a humbucker by all means. It could have rail or not have rails. Your question itself is not right.
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